Conventionally, power supply devices for air conditioners, refrigerators and the like receive alternate current (ac) voltage from commercial power supply, rectify the ac voltage by a rectifier circuit such as a diode bridge, smooth the rectified voltage by a smoothing circuit such as a capacitor to generate direct current (dc) voltage, convert the dc voltage by an inverter to ac voltage, and supply the ac voltage to an ac motor.
Such a power supply device's power factor is improved and its power supply harmonic current is reduced, by a method introducing an active filter between a rectifier circuit and a smoothing circuit to match an input current and an input voltage in waveform and phase, as described in Japanese Patent Laying-Open Nos. 2008-79474 (Patent Document 1) for example. Document 1 describes that detecting the input current, the input voltage and an output voltage and generating a signal controlling a switching element are all done by hardware (electronic circuitry).
Furthermore, there is also a method employing software to generate a signal controlling a switching element (See Japanese Patent Laying-open No. 2004-260871 (Patent Document 2) for example.). Document 2 describes that a target duty ratio is stored in an internal memory, only a voltage output from an active filter is detected, a signal controlling the switching element is generated to match the detected voltage to a target voltage, and an input current and an input voltage are not detected.